1. Field of the Invention
The present invention is related to a radio frequency identification(RFID) reader, and more particularly to a radio frequency identification capable of lowering power consumption and reducing a size by employing receiving and transmitting units of which structures are simplified.
2. Description of the Background Art
In a typical radio frequency identification (RFID) system, objects are tagged with tiny radio tags (transponders) that carry certain data about the objects. The tags (transponders) transmit this data, through radio waves, to nearby readers, which collect and process the data accordingly. These transactions between RFID tags and the readers enable a multitude of applications that require efficient detection, identification, and tracking of objects.
FIG. 1 is a block diagram showing a configuration of a conventional RFID reader. As shown in FIG. 1, the conventional RFID reader includes a controlling unit 100, a transmitting unit 110, and a receiving unit 120.
The transmitting unit 110 includes a frequency changing unit 111 changing a frequency by virtue of the controlling unit 100, a mixer 112 mixing a frequency control signal output from the controlling unit 100 and a frequency changed by the frequency changing unit 111, an amplifying unit 113 amplifying a mixed signal output from the mixer 112 to a specified level. At this point, the frequency changing unit 111 generally uses a PLL (phase locked loop) method. That is, the transmitting unit 110 modulates directly the frequency control signal output from the controlling unit 100 and a carrier frequency using an ASK (amplitude shift keying) method.
The receiving unit 120 includes a low-noise amplifying unit 121, mixers 123 and 124, a phase shifting unit 122, low pass filters 125 and 126, amplifying unit 127 and 128, high pass filters 129 and 130, and analog-to-digital converters 131 and 132.
The low-noise amplifying unit 121 amplifies a signal received from an RFID tag (not shown) to a low-noise level.
The phase shifting unit 122 shifts a phase of the changed frequency output from the frequency changing unit 111 by 90 degrees.
The mixer 123 mixes a phase-shifted-by-90 degree changed frequency and a signal output from the low-noise amplifying unit 121 to output an in-phase signal. The mixer 124 mixes a changed frequency output from the frequency changing unit 111 and a signal output from the low-noise amplifying unit 121 to output a quadrature-phase signal.
The low pass filters 125 and 126 pass the in-phase signal and the quadrature-phase signal output from the mixers 123 and 124 which are below a certain level, respectively. The amplifying units 127 and 128 amplify signals output from the low pass filters 125 and 126 to specific levels, respectively.
The analog-to-digital converters 131 and 132 convert the signals output from the amplifying unit 127 and 128 into digital signals.
The controlling unit 100 controls the changing of the frequency by the frequency changing unit 111, and generates the frequency control signal to be transmitted to the RFID tag, The controlling unit 100 analyzes a digital signal output from the receiving unit 120, and as a result recognizes data received from the RFID tag.
However, the digital data generated in the conventional RFID reader contain a lot of subharmonic components due to particular impulse characteristics, thus deteriorating frequency characteristics.
The deterioration in the frequency characteristic causes a problem of lowering performance of the RFID reader in a frequency environment where the channel bandwidth is a scarce and expensive resource.
The RFID reader using a frequency hopping method changes a central frequency of transmission signal to a preset frequency by using the PLL method. The PLL method needs a setting time for changing the frequency.
The setting time causes interruption of data communication between the RFID tag and the RFID reader, thus deteriorating the recognition rate of the RFID tag by the RFID reader.
In the conventional RFID reader, the transmitting unit uses the direct modulation method in which one PLL method is used and the receiving unit uses the direct demodulation method in which one PLL method is used.
Accordingly, the frequency of the signal received by the RFID reader and the level of the signal demodulated through a phase difference of the fixed frequency output from the PLL or by the Doppler effect change with 90 degree phase shift being made. The phase difference is demodulated using the in-phase and quadrature-phase method.
However, The demodulation using the In-phase and quadrature-phase requires that the same component be provided to each of two paths, thus making the configuration of the RFID reader complicated and increasing power consumption.